Replace setTimeout function in LastFM getPage tests

Jest fake timers don't play well with promises and setTimeout so we replace the setTimeout function and don't have to wait for the real timeout.
See jestjs/jest#7151

listenbrainz/webserver/static/js/src/LastFMImporter.test.tsx

@@ -133,19 +133,20 @@ describe("getTotalNumberOfScrobbles", () => {
 });
 
 describe("getPage", () => {
+  const originalTimeout = window.setTimeout;
   beforeAll(() => {
-    // The timeout we use in getPage's implementation does not work with Jest fake timers
-    // so we disable fake timers for this section
-    // and give enough time for the real timeouts to run
-    // see https://stackoverflow.com/questions/50783013/how-to-timeout-promises-in-jest
-    jest.useRealTimers();
-    jest.setTimeout(3000 * (LASTFM_RETRIES + 2));
+    // Ugly hack: Jest fake timers don't play well with promises and setTimeout
+    // so we replace the setTimeout function.
+    // see https://github.com/facebook/jest/issues/7151
+    // @ts-ignore
+    window.setTimeout = (fn: () => void, _timeout: number): number => {
+      fn();
+      return _timeout;
+    };
   });
 
   afterAll(() => {
-    // Back to default
-    jest.setTimeout(5000);
-    jest.useFakeTimers();
+    window.setTimeout = originalTimeout;
   });
 
   beforeEach(() => {